Finding roots of a non-rational function

Forum|Forum|15 years ago
January 24, 2011
2 replies
8520 views

Hello folks,

I have a weird problem: for some measurement data I'm trying to find the roots. This data appears to be best approximated by a sine function. As MathCad's roots/polyroots function works with rational functions only (or am I wrong on this one?) I tried to use the MATCH function together with the control parameter "near".

Weird enough, it finds only a few of the roots (see graph in the attached MC 11 file). Why doesn't it work and how could I improve this?

Thanks in advance

Raiko

1_Zeros-xmcd.zip

Statistics_Analysis

Best answer by MikeArmstrong

Slightly different approach and I have used your match function.

Mike

M

MikeArmstrong

1-Visitor

Your fitting functions doesn't look right, have you tried using the smoothing functions with Mathcad?

Mike

R

Raiko

Author

17-Peridot

Hello Mike,

yes this fitting function is an approximation by utilising a sine-function. I tried smoothing, but I'm more confident with the sine function.

Nonetheless, this doesn't solve my problem: finding the roots. Do you believe that MATCH might work better with a smoothed data set?

Thanks

Raiko

R

RichardJ

19-Tanzanite

You don't have the correct x-axis for the zero points.

The data doesn't look very sinusoidal to me. If you look at the spectrum there's at least two main frequency components. I think even two frequency components could not model that data very well though.

I have included a different approach to find the zeros using a function that finds the maxima or minima in data (I've posted this function before).

1_Zeros-xmcdz.zip